1. Field of the Invention
This invention relates to a method for refining an easily polymerizable matter-containing substance and an apparatus therefor. More particularly, it relates to a method for refining (meth)acrylic acid and/or a (meth)acrylic ester while preventing the acid and/or the ester from being polymerized particularly in the vapor phase and an apparatus to be used therefor.
2. Description of the Related Art
Such an easily polymerizable matter as impurities-containing (meth)acrylic acid has been heretofore refined as follows.
In a distillation column with a condenser and a re-boiler, the condenser is connected to the top of the distillation column via a (inter)connecting line and the re-boiler is positioned near the lower part of the distillation column via a (inter)connecting line. Here, the feed material such as the impurities-containing (meth)acrylic acid is supplied to the distillation column and distilled therein. The vapor distilled from (meth)acrylic acid which has entered the condenser via the connecting line is condensed and apart thereof is returned to the distillation column and the rest thereof is recovered as distillate D or subjected further to a subsequent treatment. Meanwhile, the liquid containing (meth)acrylic acid through the bottom of the distillation column is supplied to the re-boiler and reboiled therein, with the result that the vapor containing (meth)acrylic acid will be returned via the connecting line to the distillation column.
It is well known that (meth)acrylic acid and/or a (meth)acrylic ester is so easily polymerized very often during the process of production such as refinement and that the apparatus of production compellingly stopped. As a measure, the practice of adding a polymerization inhibitor such as hydroquinone or phenothiazine during the production of (meth)acrylic acid and/or (meth)acrylic ester thereby preventing polymerization in the liquid phase of the purification process has found popular recognition.
U.S. Pat. No. 3,988,213 discloses a method for preventing the vapor of a vinyl compound from condensing or polymerizing by providing a distillation column with a jacket.
Further, U.S. Pat. No. 3,717,553 discloses a distillation column which, by having an opening formed near the wall of a tray tower and consequently allowed to have the wall of its own wetted, is enabled to prevent a vinyl monomer from polymerizing.
Perfect prevention of the polymerization that occurs during the distillation of an easily polymerizable matter or during the condensation of a vapor or the re-condensation of the vapor in a vapor phase has not yet been accomplished.
An object of the invention is to provide a method for refining an easily polymerizable matter-containing substance such as (meth)acrylic acid and/or a (meth)acrylic ester, which attains the refinement efficiently by efficiently preventing the matter under treatment from polymerizing in a vapor phase part of a connecting line interposed between a distillation column and a heat exchanger, and an apparatus to be used therefor.
The present inventors have pursued a study and consequently found that in the distillation of (meth)acrylic acid and/or a (meth)acrylic ester, the compound being distilled is prevented from polymerizing by causing a vertical shell-and-tube heat exchanger to be supported by the distillation column and by branching a vapor line interconnecting them from the direct shell part of the distillation column or setting a condenser directly on the top of the distillation column or setting a re-boiler in the bottom of the distillation thereby decreasing the vapor phase volume thereof. This invention has been achieved as a result.
Specifically, according to the first aspect of this invention it can provide a method for refining and separating an easily polymerizable matter-containing substance by using a distillation column furnished with a heat exchanger, which method is characterized by setting the linear velocity of the vapor in a connecting line interconnecting the distillation column and the heat exchanger at a level of not less than 5 m per second and the retention time of the vapor in the connecting line at a level of not more than 3 seconds.
According to the second aspect of this invention, it can provide an apparatus for refining an easily polymerizable matter-containing substance by using a distillation column furnished with a heat exchanger, which apparatus is characterized by using a condenser as the heat exchanger and having the condenser directly set on the top of the distillation column.
Then, according to the third aspect of this invention, it can provide an apparatus for refining an easily polymerizable matter-containing substance by using a distillation column furnished with a heat exchanger, which apparatus is characterized by using a re-boiler as the heat exchanger and the re-boiler being disposed directly inside the distillation column in the lower part thereof wherein a vapor guide provided above the heating tubes for the re-boiler is opened into the vapor phase part of the column and a down-take is furnished outside the heating tubes.
As described above, this invention, in refining and separating an easily polymerizable matter-containing substance by using a distillation column furnished with a heat exchanger, is capable of effectively preventing the vapor of the easily polymerizable matter-containing substance from polymerizing by setting the linear velocity of the vapor in a (inter)connecting line interconnecting the distillation column and the heat exchanger at a level of not less than 5 m per second and the retention time of the vapor in the connecting line at a level of not more than 3 seconds.
Further, by using the apparatus of this invention for refining an easily polymerizable matter-containing substance, the vapor of the easily polymerizable matter-containing substance can be effectively prevented from polymerizing.
The above and other objects, features, and advantages of the present invention will become clear from the following description of the preferred embodiment.